1. Field of the Invention
The present invention relates to a lithography apparatus and device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred onto all or part of the substrate (e.g., a glass plate), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
In order to increase resolution limits of a lithography apparatus, while deceasing feature size, a patterning device can be used that diffracts the illumination beam to produce multiple diffraction order portions of the patterned beam of illumination. The diffraction order portions of the patterned beam interfere or combine with each other to form a final patterning beam that is projected onto the substrate. Based on an illumination mode, e.g., dipole, quadrapole, hexapole, octopole, annular, etc., and the type of patterning device being used, e.g., binary, attenuating phase shift, phase shift, alternating phase shift, the different diffraction order portions of the patterned beam will have different intensities or energies.
For example, when using dipole illumination and a binary patterning device, zero diffraction order portions of the patterned beam have significantly more energy than the first and higher diffraction order portions of the patterned beam. When the projection system combines (interferes) these different diffraction order portions of the patterned beam having the different intensities or energies, the combined patterned beam can exhibit an image contrast that is below an acceptable level. This can be caused by superfluous light that is not properly interfering in the combined patterned beam. The reduction in image contrast can result in less line width control and lower quality of a printed feature. In some cases, the low image contrast can result in features that are inoperable.
Therefore, what is needed is a system and method that increase image contrast.